Lens distortion is a generic term for perspective distortion that exists in an image. All images that are obtained, by photographing, by using a digital image capture device to some extent have lens distortion; therefore, an image that is obtained, by photographing, by using a digital image capture device is also referred to as a distorted image. Lens distortion includes types such as radial distortion, decentering distortion, and thin prism distortion, where radial distortion has greatest impact on image distortion. Radial distortion causes a point in an image to produce a radial movement relative to a distortion center, and a farther distance of a point from a distortion center indicates a larger amount of a movement. Due to existence of radial distortion, in a distorted image that is obtained, by photographing, by using a digital image capture device, a farther distance of a part from a distortion center indicates severer distortion.
In the field of image processing, a quantitative analysis method is more widely applied. When quantitative analysis is performed on a distorted image, severer image distortion caused by radial distortion indicates poorer accuracy of a quantitative analysis result. To reduce impact of radial distortion on accuracy of a quantitative analysis result, a common practice is that, radial distortion in a distorted image is first corrected and then quantitative analysis is performed on the corrected image. Correcting radial distortion may reduce image distortion, thereby improving accuracy of a quantitative analysis result. In a process of correcting radial distortion, a radial distortion parameter of a digital image capture device needs to be used. The radial distortion parameter includes a distortion coefficient and a distortion center.
In the prior art, there are multiple methods for acquiring a radial distortion parameter. In all these methods, first it is assumed that a digital image capture device conforms to a pinhole imaging model, and by moving a calibration board or the digital image capture device, the calibration board is photographed from multiple different angles to obtain multiple distorted images; an angular point of the calibration board is used as a feature point to obtain, by calculation, an intrinsic parameter of the digital image capture device; and then a radial distortion parameter is obtained according to the intrinsic parameter by using a non-linear optimization method.
After studying the prior art, the inventor finds that, a process of acquiring a radial distortion parameter by using an existing method is very complicated, in which not only a calibration board needs to be used, but also multiple images needs to be photographed. As a result, operation is inconvenient, and practicability is poor.